Argentina will use “all the tools” at its disposal to end financial speculation by grains producers and exporters, Cabinet Chief Jorge Capitanich said last week, in a further sign of state intervention in Latin America’s No. 3 economy.

Soy producers in Argentina, the world’s No. 3 soybean exporter, have been holding onto the oilseed in view of low global prices and financial uncertainty at home, depriving...